Birds of prey and owls stand on top of the food chain and thus in the end of the life cycle of many parasite species. The parasite fauna of raptorial birds in Slovakia have not been comprehensively studied and therefore there are many parasite species which are new for Slovak fauna. In addition the endangered raptorial species whose numbers are very low in Slovakia can host rare, species-specific parasites. This study was focused on the detection of the thorny-headed worms (Phylum: Acanthocephala) in birds of prey and owls in Slovakia and reviewing of their prevalence.

In years 2012 – 2014, intestines of 286 birds of prey and owls from the territory of Slovakia were examined for the presence of acanthocephalans. Sixteen falconiform bird species were examined (numbers of individuals are in brackets):  Buteo buteo (L, 1758) (n = 119), Falco tinnunculus L, 1758 (n = 73), Accipiter nisus (L, 1758) (n = 9), Aquila heliaca Savigny, 1809 (n = 6), Accipiter gentilis (L, 1758) (n = 5), Falco peregrinus Tunstall, 1771 (n = 5), Buteo rufinus (Cretzschmar, 1829) (n = 4), Buteo lagopus (Pontoppidan, 1763) (n = 5), Circus aeruginosus (L, 1758) (n = 4), Falco subbuteo L, 1758 (n = 3), Falco cherrug J.E.Gray, 1834 (n = 3), Milvus milvus (L, 1758) (n = 1), Pernis apivorus (L, 1758) (n = 1), Circus pygargus (L, 1758) (n = 1), Haliaeetus albicilla (L, 1758) (n = 1) and Falco columbarius L, 1758 (n = 1). Out of Strigiformes, seven species were dissected: Strix  uralensis Pallas, 1771 (n = 15), Asio otus (L, 1758) (n = 13), Strix aluco L, 1758 (n = 10), Tyto alba (Scopoli, 1769) (n = 3), Bubo bubo (L, 1758) (n = 2), Athene noctua (Scopoli, 1769) (n = 1), and Glaucidium passerinum (L, 1758) (n = 1). All the birds examined in this study died naturally or as a result of injury or disease. The samples came from the various locations of Slovakia. Acanthocephalan parasites were isolated from intestines of birds during parasitological autopsy, washed in tapwater and preserved in 70 % ethanol. Before species identification according to morphological characters, selected worms were cleared in glycerine or lactophenol. The species were determined using keys and papers of Meyer (1933), Petrochenko (1958), and Dimitrova et al. (1997).

Three species of thorny-headed worms of the genus Centrorhynchus were found to parasitize birds of prey and owls. Out of 286 examined bird individuals belonging to 23 species, only Buteo buteo, Buteo rufinus, Falco tinnunculus (Falconiformes), Asio otus, Strix aluco, Strix uralensis and Tyto alba (Strigiformes) were infected by acanthocephalans. All the bird species except of S. aluco represent new host records for Slovakia. The most prevalent acanthocephalan Centrorhynchus aluconis was detected in all 15 examined birds of non-migratory Ural owl S. uralensis (P=100 %), however, it was found occasionally also in two individuals of the tawny owl S. aluco (P=20 %), one long-eared owl A. otus (P=7.7 %), one barn owl T. alba (P=33.3 %), and the common buzzard B. buteo (P=0.8 %). Two other thorny-headed worms occurred exclusively in falconiforms in raw or mixed infections: Centrorhynchus buteonis was found in eleven individuals of B. buteo (P=9.2 %), and two birds (B. buteo and B. rufinus) were parasitized simultaneously by C. buteonis and the species Centrorhynchus globocaudatus. Moreover, the latest, relatively rare acanthocephalan was found alone in two common kestrels F. tinnunculus (P=2.7 %). Regarding intensity of infection, it ranged from a single female of C. buteonis, C. globocaudatus or C. aluconis per host (four cases) to maximum of 82 C. aluconis per an Ural owl. The difference in acanthocephalan species spectrum between birds of prey and owls in Slovakia was apparent. 

In Slovakia, acanthocephalans of birds of prey and owls have not been comprehensively studied. In fact, only two records were published. Ryšavý (1957) described unspecified number of males and females of C. aluconis from one S. aluco originated from vicinity of Gabčíkovo, while Škarda (1964) reported C. globocaudatus from a single red kite M. milvus from Zemplín region. Later, those ancient data have been listed in the review of Sitko (2011). Therefore, all the recent findings represent new host or geographical records for Slovakia, except for the two hitherto mentioned cases.